Deforestation, Land-Use Systems and Microclimates

Since 1984, an ongoing joint project of the International
Institute for Tropical Agriculture (IITA) and the United Nations
University has been studying the effects of deforestation on the
soils, hydrology, microclimates and biotic environments of
land-use systems abutting tropical forest. The project is being
conducted on cleared plots and adjacent high rainforest land 75
km southeast of Benin City, Nigeria. Eight types of land-use
systems are being studied, including:

Plots #2-7 were cleared using a shear blade mounted
on a bulldozer. As expected, clearing forest exerts a considerable
effect on the
microclimate. Evaporation rates were 10-12 times greater in
the cleared plots than in the control. The cleared plots also
had
higher radiation levels, lower minimum relative humidity and
higher maximum air temperatures than the forested control.
Within two years after planting, the microclimate under Cassia
siamea forest in test plot #8 was similar to that under the
natural forest. Bulk density of soil was highest in the
mechanically cleared plots even two years after initial cutting.
Steady-state infiltration rates were highest in the manually
cleared, traditionally farmed plots (304 cm/h) and lowest in the
mechanically cleared plots (47 cm/h). The surface runoff rate,
measured under forest and oil palm plots, averaged 1.34 % of the
rainfall under forest and 2.20 % of the rainfall under oil palm.
Related IITA studies using legumes (Psophorcarpus, Centrosema
and Stizolobium) as live or in situ mulches have shown
promising results in reducing this type of runoff.